It's 18 degrees outside and there are no doors or windows on their car, yet Judeth Van Hamm and Michael Connelly are all smiles as they tool around their hometown in a zero-emission vehicle that runs entirely on electricity.

The energy-conscious couple are among the first private citizens, according to the state Registry of Motor Vehicles, to have registered a "low-speed motor vehicle'' in Massachusetts - a feat they managed at the Registry's office in Braintree just hours before the New Year rang in.

The golfcart-like contraption, a Villager 2+2 made by Club Car Inc. of Augusta, Ga, can move up to 25 mph and go about 20 miles before having to be recharged, making it an ideal vehicle for short trips to the supermarket, library, and the like, said Michael Alexander, director of business development for the manufacturer.

The planet-friendly car is part of a growing trend making its way across the country, as more than half the states now have laws per mitting limited road access for such vehicles. Massachusetts joined the ranks in December 2008 with legislation cosponsored by state Senator Robert Hedlund, a Republican from Weymouth, that allows the tiny cars to travel on roads whose posted speed limits are no greater than 30 miles per hour. Most local streets are posted with a speed limit of 25 or 30 miles per hour.

The Villager 2+2 has been the fastest-growing of Club Car's vehicle sales, said Alexander. The company, a division of Ingersoll Rand, produces more than 80 on- and off-road vehicles ranging from golf carts to automobiles and trucks. Low-speed vehicles such as the Villager 2+2 have found a niche in gated communities and campus-like environments where there isn't necessarily a need for a car that can get up to highway speeds.

The price doesn't hurt either, with each vehicle costing about $10,000. And through 2009 in Massachusetts, there was a nearly 50 percent tax write-off - which was why it was so important for Van Hamm and Connelly to register the car before midnight on New Year's Eve.

"We got in just under the wire,'' Van Hamm said.

Added Connelly, "We've got to smile a little bit, and even if we didn't get the extra money back, we'd still be happy to have the vehicle.''

The couple bought their car from Country Club Enterprise in Wareham, a distributor for low-speed vehicles. Territory manager Kathy Wilkinson said last year's tax incentive brought a lot of interest from businesses wanting to go green and save money at the same time. And with the new law in place, the vehicles can now be driven off sprawling complexes down the road or across the street.

The vehicles are catching on for personal use, too. The trend has accelerated significantly as people consider their own environmental impact and look for options to use less gasoline, said Genevieve Cullen, vice president of Electric Drive Transportation Association in Washington, D.C., a trade group for a diverse alliance of companies interested in electrifying transportation.

Massachusetts is perhaps a little slower getting out the gate than other states. The Registry of Motor Vehicle's most recent count shows 10 such cars have been registered to individuals statewide. The first was registered by a Winchendon man on July 31 last year, the first day it was possible to take advantage of the tax incentive, registry spokeswoman Ann Dufresne said last week.

Massachusetts Nature Conservancy state director Steven Long says he considers the purchase of a car totally powered by electricity as a wonderful example of how to be mindful about reducing one's carbon footprint in ways that are also good for one's personal finances.

Conservancy isn't new to Van Hamm, the president of Sustainable South Shore, a 16-chapter conservation group that includes towns from Abington to Weymouth. She and Connelly also live "green,'' growing their own vegetables hydroponically with solar-generated heat that suffuses their greenhouse even in winter. And until they bought their car, they managed Hull's hilly terrain on their electric-assist bicycles, which they have relied on for most of their daily transportation.

The couple do most of their living within a 10-mile radius, using a cart attachment on their bicycles to get their weekly groceries and accepting rides or renting a car in bad weather or for long-distance travel.

They have already taken their new vehicle on errands to the local library, enjoying the friendly waves and second-looks of motorists and pedestrians. Each wheel on the car has a shock absorber, and the ride is made even smoother by its lack of a traditional car engine.

"It buzzes and turns in an interesting radius, so that you feel like you're traveling on some kind of little bug,'' said Van Hamm. The couple follow the same safety rules they've used on their bikes, pulling to the side to let drivers pass. The car is narrow enough that passing vehicles don't need to cross the center line to get by.

Low-speed vehicles like the Villager are held to pretty much the same licensing laws as more conventional cars, including a mandatory annual inspection. Figuring out what would be involved was a challenge for Van Hamm, who called around before choosing Hingham Harbor Sunoco because owner Paul DeCoste offered to make the calls to the Registry of Motor Vehicles and the car's manufacturer to find out what an inspection would entail.

Hingham police provided a solution for the couple's initial conundrum of getting their vehicle to Hingham Harbor Sunoco, which is on a road with speed limits above those set for their new vehicle. Police Sergeant David Horte escorted the couple from Nantasket Junction to the garage, where state Representative Hedlund, who had been invited by Van Hamm, and several members of the media waited.

"I didn't know it was going to be as big a deal as it was,'' said Hingham Harbor Sunoco inspector and technician Michael Galluzzo, who took about 15 minutes to check lights, blinkers, horn, and one large windshield wiper - a little less time than the usual inspection because there was no emission to check.

"It's a cool idea to get this on the road, and it would be good to get in Hull, especially, since there aren't a lot of places there where you have to go over 30 miles per hour,'' he said.

Van Hamm said she and Connelly may purchase car doors when they become available, but are happy for now to rely on their extreme-temperature parkas and matching "mad bomber'' hats. They said they are far more excited at the prospect of adding a solar panel to the roof of the vehicle, which will double its battery life.

"It's fun, it's good for the environment, and we hope to have more teammates soon,'' said Connelly.